Wireless communications systems and methods are widely used for transmitting and/or receiving information between at least two entities using a modulated carrier frequency that occupies a substantially contiguous band of frequencies over a predetermined bandwidth. For example, an Orthogonal Frequency Division Multiplexed/Multiple Access (OFDM/OFDMA) communications system and method may use a number of modulated sub-carriers which are contiguously configured in frequency so as to occupy a maximum predetermined aggregate (overall) carrier bandwidth of, for example, 1.25 MHz. Terrestrial wireless communications systems and methods may be based on cellular/PCS and/or other techniques. The overall design and operation of terrestrial wireless communications systems and methods is well known to those having skill in the art, and need not be described further herein
Satellite communications systems and methods are based on wireless communications technologies and employ at least one space-based component, such as one or more satellites, that is/are configured to communicate with a plurality of satellite radioterminals. A satellite radioterminal communications system or method may utilize a single antenna beam covering an entire area served by the system. Alternatively, in cellular satellite radioterminal communications systems and methods, multiple beams are provided, each of which can serve distinct geographical areas in the overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular/PCS radioterminal systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radioterminals over a bidirectional communications pathway, with radioterminal communication signals being communicated from the satellite to the radioterminal over a downlink or forward link, and from the radioterminal to the satellite over an uplink or return link.
The overall design and operation of cellular satellite radioterminal systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radioterminal” includes cellular and/or satellite radioterminals with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and a pager, Internet/Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “radioterminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth and/or in space. A “radioterminal” also may be referred to herein as a “radiotelephone,” “terminal”, “wireless terminal” or “wireless user device”.
Terrestrial networks can enhance cellular satellite radioterminal system availability, efficiency and/or economic viability by terrestrially reusing at least some of the frequency bands that are allocated to cellular satellite radioterminal systems. In particular, it is known that it may be difficult for cellular satellite radioterminal systems to reliably serve densely populated areas, because the satellite signal may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, the satellite spectrum may be underutilized or unutilized in such areas. The terrestrial reuse of at least some of the satellite system frequencies can reduce or eliminate this potential problem.
Moreover, the capacity of a hybrid system, comprising terrestrial and satellite-based connectivity and configured to terrestrially reuse at least some of the satellite-band frequencies, may be higher than a corresponding satellite-only system since terrestrial frequency reuse may be much denser than that of the satellite-only system. In fact, capacity may be enhanced where it may be mostly needed, i.e., in densely populated urban/industrial/commercial areas where the connectivity/signal(s) of a satellite-only system may be unreliable. As a result, a hybrid (satellite/terrestrial cellular) system that is configured to reuse terrestrially at least some of the frequencies of the satellite band may become more economically viable, as it may be able to serve more effectively and reliably a larger subscriber base.
U.S. Pat. No. 6,684,057, to inventor Karabinis, and entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a satellite frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. In particular, a system according to some embodiments of U.S. Pat. No. 6,684,057 includes a space-based component that is configured to receive wireless communications from a first radiotelephone in a satellite footprint over a satellite radiotelephone frequency band, and an ancillary terrestrial network that is configured to receive wireless communications from a second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. The space-based component also receives the wireless communications from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band as interference, along with the wireless communications that are received from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. An interference reducer is responsive to the space-based component and to the ancillary terrestrial network that is configured to reduce the interference from the wireless communications that are received by the space-based component from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band.
Satellite radioterminal communications systems and methods that may employ terrestrial reuse of satellite frequencies are also described in U.S. Pat. No. 6,785,543 to Karabinis, entitled Filters For Combined Radiotelephone/GPS Terminals, and Published U.S. Patent Application Nos. US 2003/0054761 to Karabinis, entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies; US 2003/0054814 to Karabinis et al., entitled Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0054762 to Karabinis, entitled Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems and Methods; US 2003/0153267 to Karabinis, entitled Wireless Communications Systems and Methods Using Satellite-Linked Remote Terminal Interface Subsystems; US 2003/0224785 to Karabinis, entitled Systems and Methods for Reducing Satellite Feeder Link Bandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 to Karabinis et al., entitled Coordinated Satellite-Terrestrial Frequency Reuse; US 2002/0090942 to Karabinis et al., entitled Integrated or Autonomous System and Method of Satellite-Terrestrial Frequency Reuse Using Signal Attenuation and/or Blockage, Dynamic Assignment of Frequencies and/or Hysteresis; US 2003/0068978 to Karabinis et al., entitled Space-Based Network Architectures for Satellite Radiotelephone Systems; US 2003/0153308 to Karabinis, entitled Staggered Sectorization for Terrestrial Reuse of Satellite Frequencies; and US 2003/0054815 to Karabinis, entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns In Response to Terrestrial Reuse of Satellite Frequencies, US 2004/0121727 to Karabinis, entitled Systems and Methods For Terrestrial Reuse of Cellular Satellite Frequency Spectrum In A Time-Division Duplex Mode, US 2004/0192293 to Karabinis, entitled Aggregate Radiated Power Control For Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems And Methods, US 2004/0142660 to Churan, entitled Network-Assisted Global Positioning Systems, Methods And Terminals Including Doppler Shift And Code Phase Estimates, and US 2004/0192395 to Karabinis, entitled Co-Channel Wireless Communication Methods and Systems Using Nonsymmetrical Alphabets, all of which are assigned to the assignee of the present invention, the disclosures of all of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Satellite communications systems and methods may be used for voice and/or data. Moreover, satellite communications systems and methods are increasingly being used with broadband information, such as multimedia information. Unfortunately, it may be difficult to send and receive broadband information over conventional satellite communications systems and methods.